But the ABC source said that "Birotte does not speak for the federal government as a whole," adding that the new investigation is being run out of another office.

Agents involved in Birotte's probe—which looked in charges including drug distribution, fraud and conspiracy—recommended an indictment, but the case was dropped on the Friday before the Super Bowl last year.

The evidence gathered during that investigation was used by U.S. anti-doping officials in a damning report, which prompted Armstrong's confession.

Legal experts said that the admission exposed Armstrong to possible charges of perjury or obstruction of justice.

Investigators are now looking into how Armstrong bullied and intimidated associates, including taking legal action, to conceal his doping over more than a decade.

The Telegraph notes that if federal authorities decide to prosecute, Armstrong could face jail time.